Program phase reverser



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8 Claims.

This invention relates to systems for controlling voice signals derived from a microphone or other wave pick-up device where unsymmetric electrical circuits including amplifiers are to be 5 fed by such signals. It has been observed in broadcasting and sound recording practices that the half-cycles of sound waves, particularly when produced by the human voice and by certain musical instruments. are at times considerably greater in peak amplitude in one direction or phase than in the other. When such voice waves are .impressed upon amplifiers or other apparatus having greater lee-way in one direction of swing than in the reverse, it is desirable that the maximum peaks be applied in such phase as to deliver maximum undistorted output power.

'Ihis applicationis a continuation-impart of my co-pending application, Serial No. 167,709, died October 7, 1937, for a Program polarity reone phase than in the reverse, that is,.Iinearity in one phase often extends over a greater range in one direction lthan in the reverse. Therefore, for maximum undistorted speech or program power to be transmitted through such a system', it is essential that the phasing of the voice frequency wave be made such as to place the maxi- 35 mum peaks in the direction of greatest latitude.

The human voice often has as much as a. twoto-one difference in the peak amplitudes'on the positive `and negative sides of the sound wave. In normal program work microphones of the so- 40 called velocity type are often used, and these microphones are so disposed with respect to the performers that they pick up sound waves from either one or both sides. Maximum peaks of electromotive force-excited by a human voice are 45 of one phase for one side of the microphone and the opposite for the reverse side. Ina radio broadcast program it is frequently necessary also in association with a voice frequency amplifier circuit for automatically inverting the phase of 55 vthe voice waves whenever the amplitude peaks verser. Certain improvements and simplificain one direction do not conform with the non- .linear range characteristics of the circuit.

It is a further object of my invention to provide means in a voice transmission circuit whereby maximum peaks of the voice frequency wave are applied in the direction of greatest latitude in the circuit thereby to avoid distortion.

It is a further object of my invention to provide a simple yrelay circuit arrangement under control of electron discharge tubes whereby phase reversals of the speech waves are made to take place during moments of relative silence so that no disturbance like switching plops are heard.

It is a further object of my invention to provide a program phase reversing device which will enable a microphone to be utilized under optimum conditions in connection with an amplifier or speech circuit having a non-linear characteristic such that distortion takes place at a lower p amplitude level in one direction than in the reverse; said phase reversing device being adapted to apply to said amplifier a speech wave whose unsymmetric wave peaks are suitably phased for placing these peaks in the directiony of greatest latitude. 25

My invention will now be described in more detail, reference being made to the accompanying drawing, in which the sole gure thereof represents a' circuit diagram of a preferred embodiment. Y

Referring to the drawing, I show a phase reversing system consisting essentially of a double pole double throw system, operated by suitable actuatingI apparatus. The swinging contacts a and b of relay i act as the switch blades for ac- 35 complishing the reversal.

The input transformer primary 2 bridges across the program line whose phase is to be reversed. The voltage from the secondary 3 is adjusted to proper value by potentiometer 4 and applied to 40 the grid of amplifier tube 5. Plate voltage is supe plied to tube 5 through a resistor E. Output audio voltage from tube 5 is fed through condenser 'i to a grid G in another amplifier tube 8, whose bias voltage is fed through resistor 9 from the 45 load resistors i5 and I6. The secondaries I1 55 and I8 supply' audio energy to the diode rectifier portions I9 and 20 of the discharge tube I0. These rectify opposite halves of the audio wave.- 'I'he output voltage of these rectiers appears across the resistors 2l and 22. Condensers 23 and 24, connected across these resistors store the rectified voltage for an appreciable time before being discharged by the resistors. The two recti'er output load resistors 2l and 22 are connected in series. The rectiied potentials developed across these two load resistors are opposed to one another. to the bias applied through the relay contacts d to the grid of tube 25. Audio frequency varia- 13 tions are smoothed out of this grid voltage by resistor 2@ and condenser 21. The plate current of tube 25 tends to actuate relay I. Contact c breaks away from. its back contact before the breaking of other contacts. This operation serves a0 to accelerate the action of the relay in going from the non-actuated to the actuated position. This action is accomplished by resistor 28 shunting the relay coil, thus robbing some of its current until the contact is broken. When contact 85 c closes against its front contact, then resistor 59 is placed in shunt with the space path of the tube 25 and increases the current flow through the coil oi relay i. Upon starting to de-energiae the coil, this excess current is cut ci! by opening w the circuit through resistor 59. Thus, when energizing and de-#energizing the relay the action is accelerated by the combination of relay contact connections c with resistors 28 and 29.

A duplex diode rectifier tube 50 is provided for the purpose oi forcing the reversal relay I to operate only during periods of program silence. 'I'his tube comprises two` independent space discharge paths. The electrode group 29 has an anode connected to the back contact associated with relay spring d; While the electrode group 30 has a cathode connected to the front contact as sociated with the same relay spring d. Audio signals constituting the output of `tube 8 are ted through lthe voltage dropping resistors 5I and 32 to the anode and cathode, respectively, of electrode groups 29 and 30 in tube 50. The cathode of group 29 and the anode of group 30 are connected tgether and act as the point of zero audio frequency potential connected to a D. C. bias 5 supply through a. potentiometer 25. Thus rectiied voltages are built up across resistors 35 and.

31 with opposite polarity relative to this junction of the rectifier elements. When no audio signals are being rectiiied, a suitable D. C. bias 55 potential is applied to the grid of tube 25 by virtue of the adjustment of the contact arm on potentiometer 35. With the relay in the non-actu ated position the rectified output of the electrode group 2S, negative in polarity, f is fed through the back contact and spring d of relay I. In the actuated position the rectied output of electrode group 30, positive in polarity, is fed through the front contact and spring d.

vThe lesser of the rectiiied potentials derived from audio wave peaks oi the two phases, that is, from one portion of the tube I0, are continuously subtracted from those of opposite phase, that is, as derived from the other portion of the tube I0. 'Ihis resultant voltage is .utilized in the bias circuit for the tube 25. The control bias circuit for the grid of tube may be traced from the potentiometer 35 through one or the other of the electrode. groups of tube 50, depending upon the position ofcontact d, and thence through re- 75 sistors 2|, 22 and 25 to said grid. The energy 0f amasar The resultant voltage is then added the rectified audio wave peaks is, therefore, super" posed on the D. C. bias potential in either of two ways, dependent upon the direction of unbalance between the energies stored in the capacitors 23 and 24, this being a function of the operation of tube I0. The grid bias potential is additionally dependent upon the instantaneous amplitude of the audio signal and its eiiect upon the action oi the tube 5G. These rectied potentials, therefore, serve as a control bias potential which is applied to the grid of tube 25 throughresistors 2i, 22 and 2t. The two voltages which are rectied in tube i0, filtered and stored in condensers 22 and 24, are in opposite polarity as connected, one being derived from one half of the applied audio waves, and thel other being olerived from the reverse side. Thus an unsymrnetric wave tends to cause one of these potentials to predominate over the other, giving an increase or decrease of the bias on tube 25.

in order to better illustrate the operation of the device let it be assumed that an audio wave is applied without interruption when relay I is inthe non-actuated position and that the phase oi' its dissymmetry is opposed to that of the immediately preceeding waves. Then a resultant voltage builds up across resistors 2I and 22 such that the grid end is relatively positive. However, a negative potential issupplied simultaneously from the anode of group 29 in tube et). This anode is negative and prevents the grid of tube 25 from swinging positive. Thus the relay cannot become actuated as long as the signal is applied without interruption. If, however, a momentary interruption occurs, the discharge across the electrodes 29 in tube 50 ceases instantaneously, there being no appreciable time delay circuits associated with this tube. Since the large storage condensers 23 and 24 hold the charge rectied by tube I0, this interruption causes the grid of 25 to swing positive,

thus actuating relay l and reversing the phase of the audio signal as applied to the output terminals 5I.

When the incoming wave is of opposite symmetry, the action for reversal is as follows: Voltages are built up across the storage condensers 23 and 24 such as to make the grid end of the resistors 2'I, 22 negative. However, the

rectified potential from the cathode of electrode group in tube 50 is of opposite polarity to that of the voltages stored in the condensers 23 and 24 and remains greater in magnitude as long as the incoming signal persists without interruption. 'I'he potential from the tube 50 is, in this case, applied through front contact of relay spring d to the grid control circuit for tube 25. Ii then an interruption occurs in the incoming signal the potential created by rectier tube 50 stops and the grid of tube 25 is swung negative by the previously stored potentials in condensers 23 and 24, causing the relay i to release and the phase oi the wave to be reversed in its application to the output terminais 5i.

Relay contact e serves to short circuit an indicator lamp 38 when the relay is in the nonactuated position, thus lighting lamp 39. In the actuated position of the relay. the lamp 38 is not shorted and since it is in series with lamp ,39 which is shunted by resistor 40, it is permit;

ted to have more than half oi' the total lighting voltage. 'Ihis is suiiicient to give a good indiction if lamp is covered with a blue or green applied to the end of resistor 2l approximately amasar o Resistors Il, VI2 and 4I in the cathode circuits of tubes I,- I and 25, respectively, are for purposes of metering. These resistors are low in value, but the voltage drop across any of them is sumcient for producing a reading on the meter M. The particular circuit to be metered is selected by switch 45.

Resistor Il serves to hold the bias potential thesame as that from the potentiometer I5 while the relay contact d is traveling from front to back contacts and vice versa.

Resistors 41 and Il are of relatively high ohmic valueand serve to bridge the contact groups a and b, respectively. Ihis is to prevent click noises caused by the input and output circuits assuming different D. C. potentials while switching.

It will be apparent to those skilled in the art that a single amplifier tube might be substituted for the double tube 8. Such a substitution involves merely the adoption of a-singie-anode output circuit in place of the pushpull circuit shown. Furthermore, the tube I0 might be supplied with energy derived solely from one side, or one anode, of the audio wave amplier.

By comparison with the disclosure of my aforementioned co-pending application, Serial No. 167,709. it will be seen that the instant disclosure presents an embodiment of the invention which is simpler to construct and more economical to maintain. 'I'he operation of the device is obtained under improved conditions of emciency. In the first disclosure of the invention it appeared to be necessary to employ as many as three electromagnetic relays. The same functions are now performed bya single electromagnetic relay. The apparatus, therefore, meets. the exacting requirements for reversibly switching the connections between two input terminals and two output terminals without introducing any appreciable plops into the speech circuit in which it is preferably employed.

My invention is capable of modication in a number of different ways such as might suggest themselves to those skilled ln the art. 'I'he scope of the invention is, therefore, deiined byV the claims.

I claim:

1. In a switching arrangement for reversing the connections between two inputv terminals and two output terminals, a relay having operable contacts for making said connections reversibly, means including an electron discharge tube rectiiler and an electrostatic storage device for building up a'relay energizing force in-response to a dissymmetry of audio frequency currents impressed upon said input terminals, and in eans including a second electron discharge tube rectiller operative in dependence upon the amplitude level of said currentsr for restraining the operation of said relay untilsaid amplitude level falls' to a predeterminedA critical value.

2. Apparatus in accordance with claim land having means including additional contacts oper- .able by said relay and connected through the winding thereof for accelerating its action.

3. In switching apparatus for reversing the connections between two input terminals and two output terminals, a single electromagnetic relay having operable contacts for making said connections reversibly. an electron discharge tube circuit arrangement adapted to amplify and to rectify certain components of an audio frequency .current impressed upon said input terminals,

means for storing the resultant of opposing rectitled components derived from dissymmetries of said current, additional rectifying means operable in dependence upon the reduction of said audio frequency current to a. predetermined low level for timing the operation of said relay so as to coincide with periods of substantially no current applied to said input terminals, means including other contacts of said relay constituting a single pole double throw switch for connecting said additional rectlfying means in aiding or opposing relation to, said storing means in accordance with the condition of said relay, and means including a discharge tube in series with the winding of said relay for controlling the times of energizing and de-energiaingthe same, the last said discharge tube having a grid biasing circuit which includes a direct current source. said additional rectifying means, the single pole double throw switch contacts of said relay and said storing means.

4. In a circuit arrangement having input and output terminals, a first rectifier means, a second rectifier means and a solitary relay the winding of which is in series with the space path of an electron discharge tube. the method of controlling the operation of said 'relay' thereby to cause its contacts to reverse the connections between said input and output terminals, which comprises the steps of separately storing the energies delived from the rectification in said first rectifying means of opposing half cycles of an unsymmetric audio wave, rectifying a portion of the energy derived from said audio wave in said second rectifying means for producing a substantially instantaneous response characteristic of differences in the overall amplitude of said audio wave and applying a bias control potential to said electron discharge tube which is the resultant of a xed bias, a bias determined by said second rectifying means and a bias constituting the difference between the separately stored energies. thereby to produce alternate blocking and discharge conditions in. said tube and to reversibly actuate said relay. v

5. In an audio frequency circuit arrangement having two input and two output terminals, apparatus foi' reversing the connections between said terminals, said apparatus being operative in response to a reversal in the direction of phase dissymmetry of an audio wave impressed upon said input terminals, a pair of mutually opposing 'half wave rectiers connected to said input terminals, capacitive and resistive means for momentarily storing ldilferences between the energies thus rectified, an electron discharge tube having an input circuit including a second rectifier in circuit lwith a direct current grid biasing source and with said capacitive means, said second rectifier being of the double-diode type and responsive to instantaneous variations in the amplitude of said audio wave, a relay having circuit reversing contacts for completing the rst mentioned connections, means including other reversing contacts of said relay for causing said second rectifier to aid o r oppose the biasing effect of said storage means, and means including operative connections through said discharge tube and the coil of said relay for causing said input and output terminal connections to be reversed only when a moment of substantially zero am- 1 havingmeans for accelerating the action of said.

relay, said means comprising a resistor in circuit lwith a pair of contacts of said relay and in shunt with the discharge tube whose space path is in series with the coil of said relay, whereby, upon opening said contacts, the energy fed through said coil is suddenly reduced.

8. An electromagnetic relay having contacts constituting a double pole double throw switch,

said contacts providing reversible connections between two input .terminals and two outputterL1 minals of an audio wave circuit;meansi'orl enu ergizing and de-energizing said relay in response to changes in the direction of phasemdissymmetry oi the audio frequency wave impressed upon said input terminals, said means including. a pair of mutually opposing half wave rectiners connected to said input terminals, a device for momentarily storing the diiieretial component ortheoutput energies from said rectiiiers, means operative by the resultant oi' said dierential component for increasing and reducing thereiay, energizingy cur rent in dependence upon the direction of shift' of said phase dissymmetry, and means controlled by the amplitude of said wave for delaying the action of said relay until a moment of substantially zero current occurs in said audio Wave.

JARRE'IT L. HATHAWAY. 

